Phosphine substituted ferrocenyl complex

ABSTRACT

A functionalized magnetic nanoparticle including an organometallic sandwich compound and a magnetic metal oxide. The functionalized magnetic nanoparticle may be reacted with a metal precursor to form a catalyst for various C—C bond forming reactions. The catalyst may be recovered with ease by attracting the catalyst with a magnet.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of Ser. No. 15/610,269, nowallowed, having a filing date of May 31, 2017 which claims benefit ofpriority of U.S. Provisional Application No. 62/406,449 having a filingdate of Oct. 11, 2016, incorporated herein by reference in its entirety.

STATEMENT OF FUNDING ACKNOWLEDGMENT

This project was funded by the National Plan for Science, Technology andInnovation (MAARIFAH)-King Abdulaziz City for Science and Technologythrough the Science and Technology Unit at King Fahd University ofPetroleum and Minerals (KFUPM), the Kingdom of Saudi Arabia, awardnumber 15-NAN4650-04.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTORS

Aspects of this technology are described in an article “Magneticnanoparticle-supported ferrocenylphosphine: a reusable catalyst forhydroformylation of alkene and Mizoroki-Heck olefination” by M.Nasiruzzaman Shaikh, Md. Abdul Aziz, Aasif Helal, Mohamed Bououdina,Zain H. Yamania, and Tae-Jeong Kim, in RSC Advances, 2016, pages41687-41695, which is incorporated herein by reference in its entirety.

BACKGROUND Field of the Disclosure

The present disclosure relates to a functionalized magnetic nanoparticleincluding an organometallic sandwich compound and a functional groupwhich can bind to a nanoparticle. The disclosure also relates to amagnetic catalyst which catalyzes C—C bond forming reactions such ashydroformylation and the Mizoroki-Heck coupling reaction.

Description of the Related Art

Carbon-carbon bond formation reactions mediated by various transitionmetals have emerged as increasingly important methodologies for thepreparation of numerous organic building blocks for drugs, pesticides,dye, and natural products (M. A. Gauthier, H.-A. Klok, Chem. Commun. 23(2008) 2591-2611; D.-W. Ryu, D. N. Primer, J. C. Tellis, G. A Molander,Chem. Eur. J. 22 (2016) 120-123; A. Brennfuhrer, H. Neumann, M. Beller,Angew. Chem. Int. Ed. 48 (2009) 4114-4133; T. Rybak, D. G Hall, Org.Lett. 17 (2015) 4156-4159; and R. Liu, M. Zhang, T. P. Wyche, G. N.Winston-McPherson, T. S. Bugni, W. Tang, Angew. Chem., Int. Ed. 51(2012) 7503-7506, each incorporated herein by reference in theirentirety). Among the many frequently used C—C bond formation protocols,such as Stille, Heck, Suzuki, Kumada, and Sonogashira, Mizoroki-Heck forolefination and alkene hydroformylation to the corresponding aldehydeare important in synthetic organic and industrial chemistry (J. K.Stille, Angew. Chem. Int. Ed. 25 (1986) 508-524; R. F. Heck, Acc. Chem.Res. 12 (1979) 146-151; N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995)2457-2483; A. Suzuki, Chem. Commun. (2005) 4759-4763; K. Tamao, K.Sumitani, M. Kumada, J. Am. Chem. Soc. 94 (1972) 4374-4376; T. W. Lyons,M. S. Sanford, Chem. Rev. 110 (2010) 1147-1169; S. Sobhani, Z.Pakdin-Parizi, Applied Catalysis A: General 479 (2014) 112-120; F.Ungvary, Coord. Chem. Rev. 251 (2007) 2087-2102, each incorporatedherein by reference in their entirety). Mizoroki-Heck reactions areoften catalyzed by different phosphine-based homogeneous Pd metalcomplexes. For example, PPh₃, P(o-Tol)₃ and P(Mes)₃ are used asmonodentate ligands, and dippb (1,4-bis[(diisopropyl)phosphino]butane),dippp (1,4-bis[(diisopropyl)phosphino]propane) and dppf(1,1′-bis(diphenylphosphino)ferrocene) are considered bidentate ligands(H. A. Dieck, R. F. Heck, J. Am. Chem. Soc. 96 (1974) 1133-1136; R. F.Heck, Pure & Appl. Chem. 50 (1978) 691-701; W. A. Heinnann, C. Brobmer,K. Ofele, M. Belier, H. Fischer, J. Mol. Catal. A: Chem. 103 (1995)133-146; Y. Bendavid, M. Portnoy, M. Gozin, D. Milstein, Organometallics11 (1992) 1995-1996; M. Portnoy, Y. Bendavid, D. Milstein,Organometallics 12 (1993) 4734-4735; and T. Jia, P. Cao, B. Wang, Y.Lou, X. Yin, M. Wang, J. Liao, J. Am. Chem. Soc. 137 (2015) 13760-13763,each incorporated herein by reference in their entirety). In a similarfashion, Co-, Rh- and Ir-based metal complexes have been used forhydroformylation in the presence of syngas and provide highregioselectivities (C. Godard, S. B. Duckett, S. Polas, R. Tooze, A. C.Whitwood, Dalton Trans. 14 (2009) 2496-2509; C. Kubis, M. Sawall, A.Block, K. Neymeyr, R. Ludwig, A. Berner, D. Selent, Chem. Eur. J. 20(2014) 11921-11931; I. Piras, R. Jennerjahn, R. Jackstell, A.Spannenberg, R. Franke, M. Beller, Angew. Chem. Int. Ed. 50 (2011)280-284, each incorporated herein by reference in their entirety).However, the separation of the catalyst from the reaction mixture bychromatography, distillation, and extraction is highly tedious,cumbersome, and economically less viable. In addition, the valuablemetal and ligands used in the process are not recoverable or reusable,which limits the scope of this process for cost-effective application.

In this context, the development of environmentally benign, reusable,and efficient organocatalysts is the central goal in current research tocontribute towards a ‘greener’ and safe environment. Moreover, the useof a readily available feedstock, such as carbon monoxide, to producemore expensive functionalized organic intermediates via hydroformylationis important. Therefore, extensive efforts have been focused on thedevelopment of alternatives to homogeneous catalysis to minimizeseparation costs and maximize product purity. One of the options isheterogeneous catalysis (W. Dai, Y. Zhang, Y. Tan, X. Luo, X. Tu,Applied Catalysis A: General 514 (2016) 43-50; and R. Abu-Reziq, H.Alper, D. Wang, M. L. Post, J. Am. Chem. Soc. 128 (2006) 5279-5282, eachincorporated herein by reference in their entirety). The method formaking heterogeneous catalysts is based on the immobilization of ligandsor metal complexes over solid supports, such as zeolites, polymers,silica and cellulose (Z.-M. Li, Y. Zhou, D.-J. Tao, W. Huang, X.-S.Chen, Z. Yang, RSC Adv. 4 (2014) 12160-12167; H. Zhang, W. Yang, J.Deng, Polymer 80 (2015) 115-122; A. R. McDonald, C. Müller, D. Vogt, G.P. M. van Klink, G. van Koten, Green Chem. 10 (2008) 424-432; and S.Zhou, M. Johnson, J. G. C. Veinot, Chem. Commun. 46 (2010) 2411-2413,each incorporated herein by reference in their entirety). For example,Koten et al. demonstrated the anchoring of chiral BINAP ligands on thesurface of silica, which is highly stable, robust and easy tofunctionalize for the hydrogenation reaction. Recently, Wang et al.developed a heterocyclic carbene ligand-coated magnetic system andreported encouraging results for the coupling reaction (Z. Wang, Y. Yu,Y. X. Zhang, S. Z. Li, H. Qian, Z. Y. Lin, Green Chem. 17 (2015)413-420, incorporated herein by reference in its entirety). However, themajority of the heterogeneous catalysts exhibit lower reactivitycompared to that of their homogeneous counterpart because the catalyticsites can be obstructed by the solid support and become inaccessible tothe substrate, decreasing the overall catalytic activity (V.Polshettiwar, B. Baruwati, R. S. Varma, Chem. Commun. (2009) 1837-1839;and R. S. Varma, Pure & Appl. Chem. 85 (2013) 1703-1710, eachincorporated herein by reference in their entirety). Furthermore, solidcatalyst separation processes, such as filtration, emulsification, andcentrifugation, are complex, and can thus affect the activity and reducethe potential reusability of conventional heterogeneous catalysts (S.Vellalath, I. Coric, B. List, Angew. Chem. Int. Ed. 49 (2010) 9749-9752;and M. Gemmeren, F. Lay, B. List, Aldrichim. Acta 47 (2014) 3-13, eachincorporated herein by reference in their entirety).

In view of the foregoing, an objective of the present disclosure is toprovide a heterogeneous catalyst with an activity comparable to that ofa homogenous catalyst. It is a further objective to provide aheterogeneous catalyst which can be separated from the reaction mixturewith ease and which can be recycled with minimal loss in catalyticactivity.

SUMMARY OF THE DISCLOSURE

A first aspect of the disclosure relates to a complex represented byFormula (IA), Formula (IB), Formula (IIA), or Formula (IIB), a solvate,or a stereoisomer thereof, wherein Formula (IA), Formula (IB), Formula(IIA), or Formula (IIB) are:

where each of R¹, R², R³, R⁴, and R⁵ is independently a hydrogen, anoptionally substituted alkyl, an optionally substituted cycloalkyl, anoptionally substituted aryl, or an optionally substituted arylalkyl;

R^(5′) is a hydrogen, hydroxy, cyano, nitro, an optionally substitutedalkyl, an optionally substituted cycloalkyl, an optionally substitutedaryl, an optionally substituted arylalkyl, an optionally substitutedalkoxy, an optionally substituted cycloalkyloxy, an optionallysubstituted aryloxy, an optionally substituted arylalkoxy, or anoptionally substituted carbamyl;

each of R⁶ and R⁷ is independently a hydrogen, cyano, nitro, anoptionally substituted alkyl, an optionally substituted cycloalkyl, anoptionally substituted aryl, an optionally substituted arylalkyl, anoptionally substituted alkoxy, an optionally substituted cycloalkyloxy,an optionally substituted aryloxy, or an optionally substitutedcarbamyl;

each of R⁸ is an optionally substituted alkyl, an optionally substitutedcycloalkyl, an optionally substituted aryl, or an optionally substitutedarylalkyl;

a and b are independently an integer in a range of 1-10;

X is O or NH;

M is selected from the group consisting of chromium, nickel, iron, lead,ruthenium, and rhodium; and

W is an optionally subsituted arylene.

In one embodiment, M is iron.

In one embodiment, R¹ is an optionally substituted alkyl.

In one embodiment, R⁸ is an optionally substituted aryl.

In one embodiment, X is NH.

In one embodiment, the complex is:

A second aspect of the disclosure relates to a functionalized magneticnanoparticle, comprising: (i) a complex represented by Formula (IIIA),Formula (IIIB), Formula (IVA), or Formula (IVB), a solvate, or astereoisomer thereof; and (ii) a nanoparticle comprising at least onemagnetic metal oxide selected from the group consisting of nickel(II)oxide, chromium(IV) oxide, manganese(II) oxide, manganese(III) oxide,iron(II) oxide, and iron(III) oxide;

wherein the complex represented by Formula (IIIA), Formula (IIIB),Formula (IVA), or Formula (IVB) is:

where each of R¹, R², R³, and R⁴ is independently a hydrogen, anoptionally substituted alkyl, an optionally substituted cycloalkyl, anoptionally substituted aryl, or an optionally substituted arylalkyl;

each of R⁶ and R⁷ is independently a hydrogen, cyano, nitro, anoptionally substituted alkyl, an optionally substituted cycloalkyl, anoptionally substituted aryl, an optionally substituted arylalkyl, anoptionally substituted alkoxy, an optionally substituted cycloalkyloxy,an optionally substituted aryloxy, or an optionally substitutedcarbamyl;

each of R⁸ is an optionally substituted alkyl, an optionally substitutedcycloalkyl, an optionally substituted aryl, or an optionally substitutedarylalkyl;

R⁹ is a single bond, a hydrogen, an optionally substituted alkyl, anoptionally substituted cycloalkyl, an optionally substituted aryl, or anoptionally substituted arylalkyl;

R^(9′) is a —O—, hydrogen, hydroxy, cyano, nitro, an optionallysubstituted alkyl, an optionally substituted cycloalkyl, an optionallysubstituted aryl, an optionally substituted arylalkyl, an optionallysubstituted alkoxy, an optionally substituted cycloalkyloxy, anoptionally substituted aryloxy, an optionally substituted arylalkoxy, oran optionally substituted carbamyl;

a and b are independently an integer in a range of 1-10;

X is O or NH;

M is selected from the group consisting of chromium, nickel, iron, lead,ruthenium, and rhodium;

W is an optionally subsituted arylene; and

wherein an oxygen atom in —OR⁹ group in the complex represented byFormula (IIIA), Formula (IIIB), Formula (IVA), or Formula (IVB) is boundto a surface of the nanoparticle.

In one embodiment, the nanoparticle comprises iron(II) oxide andiron(III) oxide.

In one embodiment, the nanoparticle has an average diameter in a rangeof 1-20 nm.

In one embodiment, the average diameter of the nanoparticle is in arange of 6-8 nm.

In one embodiment, the functionalized magnetic nanoparticle has asaturation magnetization in a range of 40-70 emu/g.

A third aspect of the disclosure relates to a catalyst, comprising areaction product of the functionalized magnetic nanoparticle of thesecond aspect and a palladium complex or a rhodium complex, wherein thecatalyst comprises palladium or rhodium bound to a phosphorous atom inat least one —PR⁸ ₂ group.

In one embodiment, the complex is:

In one embodiment, the catalyst has a saturation magnetization in arange of 30-70 emu/g.

In one embodiment, the catalyst retains at least 90% of an initialcatalytic activity when the catalyst is reused.

A fourth aspect of the disclosure relates to a hydroformylation method,comprising reacting an optionally substituted alkene with carbonmonoxide and hydrogen in the presence of the catalyst of the thirdaspect and optionally a solvent thereby forming an aldehyde, wherein thecatalyst comprises rhodium bound to a phosphorous atom in at least one—PR⁸ ₂ group.

In one embodiment, the reacting is carried out at a pressure in a rangeof 100-1,000 psi for 5-20 hours at a temperature in a range of 40-80°C., the solvent is present, and the solvent comprises DCM, THF, or both.

In one embodiment, the method further comprises separating the catalystfrom the aldehyde, and reusing the catalyst.

A fifth aspect of the disclosure relates to a Mizoroki-Heck couplingmethod, comprising reacting an optionally substituted styrene with anaryl halide in the presence of the catalyst of the third aspect, asolvent, and a base thereby forming a coupling product, wherein thecatalyst comprises palladium bound to a phosphorous atom in at least one—PR⁸ ₂ group.

In one embodiment, the reacting is carried out at a temperature in arange of 50-100° C. for 10 minutes to 30 hours, the solvent comprises atleast one selected from the group consisting of DMF, water, and toluene,and the base comprises at least one selected from the group consistingof an alkali metal hydroxide, an alkali metal carbonate, and an amine.

In one embodiment, the method further comprises separating the catalystfrom the coupling product, and reusing the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is a reaction scheme for the synthesis of Fe₃O₄@dop-BPPF-Pd andFe₃O₄@dop-BPPF-Rh.

FIG. 1B is a transmission electron micrograph of Fe₃O₄.

FIG. 1C is a transmission electron micrograph of Fe₃O₄@dop-BPPF.

FIG. 1D is a transmission electron micrograph of Fe₃O₄@dop-BPPF-Pd.

FIG. 1E is a transmission electron micrograph of Fe₃O₄@dop-BPPF-Rh.

FIG. 1F is a high resolution transmission electron micrograph ofFe₃O₄@dop-BPPF-Pd.

FIG. 1G is a selected area electron diffraction (SAED) pattern ofFe₃O₄@dop-BPPF-Pd.

FIG. 2 is an overlay of the XRD patterns of Fe₃O₄, Fe₃O₄@dop-BPPF,Fe₃O₄@dop-BPPF-Pd, and Fe₃O₄@dop-BPPF-Rh.

FIG. 3A is an elemental map of iron in Fe₃O₄@dop-BPPF.

FIG. 3B is an elemental map of phosphorous in Fe₃O₄@dop-BPPF.

FIG. 3C is an elemental map of palladium in Fe₃O₄@dop-BPPF-Pd.

FIG. 3D is an elemental map of rhodium in Fe₃O₄@dop-BPPF-Rh.

FIG. 4A illustrates the magnetic hysteresis loops of Fe₃O₄,Fe₃O₄@dop-BPPF, Fe₃O₄@dop-BPPF-Pd, and Fe₃O₄@dop-BPPF-Rh at roomtemperature with a 1 tesla magnet.

FIG. 4B shows the Fe₃O₄@dop-BPPF-Rh particles in the vial are attractedto the magnet placed outside the vial.

FIG. 5 is a graph illustrating the conversion of Mizoroki-Heck reactionscatalyzed by a recycled catalyst.

FIG. 6 is a reaction scheme for the synthesis of dop-BPPF.

FIG. 7 is a ¹H NMR spectrum of dop-BPPF in DMSO-d₆.

FIG. 8 is a ¹P NMR spectrum of dop-BPPF in DMSO-d₆.

FIG. 9 is a fast atom bombardment (FAB) mass spectrum of dop-BPPF.

FIG. 10 is a thermogravimetry curve of Fe₃O₄@dop-BPPF under argonatmosphere.

FIG. 11 is an overlay of FT-IR spectra of Fe₃O₄, dop-BPPF, andFe₃O₄@dop-BPPF.

FIG. 12A is an overlap of the experimental and refined XRD patterns ofFe₃O₄.

FIG. 12B shows the difference between the refined and experimental XRDpatterns of Fe₃O₄.

FIG. 13A is an overlap of the experimental and refined XRD patterns ofFe₃O₄@dop-BPPF.

FIG. 13B shows the difference between the refined and experimental XRDpatterns of Fe₃O₄@dop-BPPF.

FIG. 14A is an overlap of the experimental and refined XRD patterns ofFe₃O₄@dop-BPPF-Pd.

FIG. 14B shows the difference between the refined and experimental XRDpatterns of Fe₃O₄@dop-BPPF-Pd.

FIG. 15A is an overlap of the experimental and refined XRD patterns ofFe₃O₄@dop-BPPF-Rh.

FIG. 15B shows the difference between the refined and experimental XRDpatterns of Fe₃O₄@dop-BPPF-Rh.

FIG. 16A is an energy dispersive X-ray (EDX) spectrum ofFe₃O₄@dop-BPPF-Rh.

FIG. 16B is an EDX spectrum of Fe₃O₄@dop-BPPF-Pd.

FIG. 17 is a gas chromatogram of the hydroformylated products of styreneformed in DCM at 45° C.

FIG. 18 is a mass spectrum of the branched aldehyde formed byhydroformylating styrene.

FIG. 19 is a mass spectrum of the hydroformylated products of styreneformed in THF at 45° C.

FIG. 20 is a gas chromatogram of the linear aldehyde formed byhydroformylating styrene.

FIG. 21 is a gas chromatogram of the hydroformylated products of4-methylstyrene formed in DCM at 45° C.

FIG. 22 is a mass spectrum of the branched aldehyde formed byhydroformylating 4-methylstyrene.

FIG. 23 is a mass spectrum of the linear aldehyde formed byhydroformylating 4-methylstyrene.

FIG. 24 is a gas chromatogram of the hydroformylated products of4-methylstyrene formed in THF at 45° C.

FIG. 25 is a gas chromatogram of the hydroformylated products of4-vinylanisole formed in DCM at 45° C.

FIG. 26 is a mass spectrum of the branched aldehyde formed byhydroformylating 4-vinylanisole.

FIG. 27 is a mass spectrum of the linear aldehyde formed byhydroformylating 4-vinylanisole.

FIG. 28 is a gas chromatogram of the hydroformylated products of4-chlorostyrene formed in DCM at 45° C.

FIG. 29 is a mass spectrum of the branched aldehyde formed byhydroformylating 4-chlorostyrene.

FIG. 30 is a mass spectrum of the linear aldehyde formed byhydroformylating 4-chlorostyrene.

FIG. 31 is a gas chromatogram of the hydroformylated products of3-nitrostyrene formed in DCM at 45° C.

FIG. 32 is a mass spectrum of the branched aldehyde formed byhydroformylating 3-nitrostyrene.

FIG. 33 is a mass spectrum of the linear aldehyde formed byhydroformylating 3-nitrostyrene.

FIG. 34 is a gas chromatogram of the hydroformylated products of2-bromostyrene formed in DCM at 45° C.

FIG. 35 is a mass spectrum of the branched aldehyde formed byhydroformylating 2-bromostyrene.

FIG. 36 is a mass spectrum of the linear aldehyde formed byhydroformylating 2-bromostyrene.

FIG. 37 is a gas chromatogram of the Mizoroki-Heck reaction product ofstyrene and iodobenzene formed at 95° C.

FIG. 38 is a mass spectrum of iodobenzene at Rt=7.585 minutes.

FIG. 39 is a mass spectrum of the coupling reaction product of styreneand iodobenzene.

FIG. 40 is a gas chromatogram of the Mizoroki-Heck reaction product ofstyrene and bromobenzene formed at 95° C. after 1 hour.

FIG. 41 is a mass spectrum of bromobenzene at Rt=5.055 minutes.

FIG. 42 is a gas chromatogram of the Mizoroki-Heck reaction product ofstyrene and bromobenzene formed at 95° C. after 2 hours.

FIG. 43 is a gas chromatogram of the Mizoroki-Heck reaction product of4-methylstyrene and iodobenzene formed at 95° C.

FIG. 44 is a mass spectrum of the Mizoroki-Heck reaction product of4-methylstyrene.

FIG. 45 is a gas chromatogram of the Mizoroki-Heck reaction product of4-methylstyrene and bromobenzene formed at 95° C. after 30 minutes.

FIG. 46 is a gas chromatogram of the Mizoroki-Heck reaction product of4-methylstyrene and bromobenzene formed at 95° C. after 2 hours.

FIG. 47 is a gas chromatogram of the Mizoroki-Heck reaction product of4-vinylanisole and iodobenzene formed at 95° C. after 30 minutes.

FIG. 48 is a mass spectrum of the Mizoroki-Heck coupling reactionproduct of 4-vinylanisole.

FIG. 49 is a gas chromatogram of the Mizoroki-Heck reaction product of4-vinylanisole and bromobenzene formed at 95° C. after 1 hour.

FIG. 50 is a gas chromatogram of the Mizoroki-Heck reaction product of4-chlorostyrene and iodobenzene formed at 95° C. after 30 minutes.

FIG. 51 is a mass spectrum of the Mizoroki-Heck coupling reactionproduct of 4-chlorostyrene.

FIG. 52 is a gas chromatogram of the Mizoroki-Heck reaction product of4-chlorostyrene and bromobenzene formed at 95° C. after 1 hour.

FIG. 53 is a gas chromatogram of the Mizoroki-Heck reaction product of3-nitrostyrene and iodobenzene formed at 95° C. after 30 minutes.

FIG. 54 is a mass spectrum of the Mizoroki-Heck coupling reactionproduct of 3-nitrostyrene.

DETAILED DESCRIPTION OF THE DISCLOSURE

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

As used herein, the words “a”, “an”, and the like carry the meaning of“one or more”. Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

The present disclosure is further intended to include all isotopes ofatoms occurring in the present compounds. Isotopes include those atomshaving the same atomic number but different mass numbers. By way ofgeneral example, and without limitation, isotopes of hydrogen includedeuterium and tritium. Isotopes of carbon include ¹³C and ¹⁴C.Isotopically labeled compounds of the disclosure can generally beprepared by conventional techniques known to those skilled in the art orby processes and methods analogous to those described herein, using anappropriate isotopically labeled reagent in place of the non-labeledreagent otherwise employed.

The first aspect of the disclosure relates to the complex represented byFormula (IA), Formula (IB), Formula (IIA), or Formula (IIB):

Each of R¹, R², R³, R⁴, and R⁵ is independently a hydrogen, anoptionally substituted alkyl, an optionally substituted cycloalkyl, anoptionally substituted aryl, or an optionally substituted arylalkyl. Insome embodiments, R′ is an optionally substituted alkyl. Preferably, R¹is methyl. In preferred embodiments, R², R³, R⁴, and R⁵ are hydrogens.

R^(5′) is a hydrogen, hydroxy, cyano, nitro, an optionally substitutedalkyl, an optionally substituted cycloalkyl, an optionally substitutedaryl, an optionally substituted arylalkyl, an optionally substitutedalkoxy, an optionally substituted cycloalkyloxy, an optionallysubstituted aryloxy, an optionally substituted arylalkoxy, or anoptionally substituted carbamyl. In preferred embodiments, R^(5′) is ahydroxy group.

Each of R⁶ and R⁷ is independently a hydrogen, cyano, nitro, anoptionally substituted alkyl, an optionally substituted cycloalkyl, anoptionally substituted aryl, an optionally substituted arylalkyl, anoptionally substituted alkoxy, an optionally substituted cycloalkyloxy,an optionally substituted aryloxy, or an optionally substitutedcarbamyl. Preferably, R⁶ and R⁷ are hydrogens.

Each of R⁸ is an optionally substituted alkyl, an optionally substitutedcycloalkyl, an optionally substituted aryl, or an optionally substitutedarylalkyl. In some embodiments, R⁸ is an optionally substituted aryl.Preferably, R⁸ is phenyl.

The term “alkyl”, as used herein, unless otherwise specified, refers toa straight, branched, or cyclic hydrocarbon fragment. Non-limitingexamples of such hydrocarbon fragments include methyl, ethyl, propyl,isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl,hexyl, isohexyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl.As used herein, the term “cyclic hydrocarbon” refers to a cyclized alkylgroup. Exemplary cyclic hydrocarbon (i.e. cycloalkyl) groups include,but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, norbornyl, and adamantyl. Branched cycloalkyl groups, suchas exemplary 1-methylcyclopropyl and 2-methycyclopropyl groups, areincluded in the definition of cycloalkyl as used in the presentdisclosure.

The term “aryl”, as used herein, and unless otherwise specified, refersto a substituent that is derived from an aromatic hydrocarbon (arene)that has had a hydrogen atom removed from a ring carbon atom. Arylincludes phenyl, biphenyl, naphthyl, anthracenyl, and the like.

As used herein, the term “substituted” refers to compounds where atleast one hydrogen atom is replaced with a non-hydrogen group, providedthat normal valencies are maintained and that the substitution resultsin a stable compound. When a compound or a R group (denoted as R¹, R²,and so forth) is noted as “optionally substituted”, the substituents areselected from the exemplary group including, but not limited to, alkyl;alkoxy (i.e., straight or branched chain optionally substituted alkoxyhaving 1 to 10 carbon atoms, and includes, for example, methoxy, ethoxy,propoxy, isopropoxy, butoxy, isobutoxy, secondary butoxy, tertiarybutoxy, pentoxy, isopentoxy, hexyloxy, heptyloxy, octyloxy, nonyloxy,and decyloxy); cycloalkyloxy (i.e., cyclopentyloxy, cyclohexyloxy, andcycloheptyloxy); aryloxy including an optionally substituted phenoxy;arylalkyloxy (e.g., benzyloxy); an optionally substituted hydrocarbyl;arylalkyl; hydroxy; amino; alkylamino; arylamino; arylalkylamino;disubstituted amines (e.g., in which the two amino substituents areselected from the exemplary group including, but not limited to, alkyl,aryl, or arylalkyl); arylamino; substituted arylamino; nitro; cyano;carbamyl (e.g. —CONH₂), substituted carbamyl (e.g. —CONHalkyl,—CONHaryl, —CONHarylalkyl or cases where there are two substituents onone nitrogen from alkyl, aryl, or arylalkyl); aryl; substituted aryl;and mixtures thereof and the like. The substituents may be eitherunprotected, or protected as necessary, as known to those skilled in theart, for example, as taught in Greene, et al., “Protective Groups inOrganic Synthesis”, John Wiley and Sons, Second Edition, 1991, herebyincorporated by reference in its entirety).

The term “arylalkyl” as used in this disclosure refers to a straight orbranched chain alkyl moiety having 1 to 8 carbon atoms that issubstituted by an aryl group or a substituted aryl group having 6 to 12carbon atoms, and includes benzyl, 2-phenethyl, 2-methylbenzyl,3-methylbenzyl, 4-methylbenzyl, 2,4-dimethylbenzyl,2-(4-ethylphenyl)ethyl, 3-(3-propylphenyl)propyl.

The term “hydrocarbyl” as used herein refers to a univalent hydrocarbongroup containing up to about 24 carbon atoms (i.e., a group containingonly carbon and hydrogen atoms) and that is devoid of olefinic andacetylenic unsaturation, and includes alkyl, cycloalkyl,alkyl-substituted cycloalkyl, cycloalkyl-substituted cycloalkyl,cycloalkylalkyl, aryl, alkyl-substituted aryl, cycloalkyl-substitutedaryl, arylalkyl, alkyl-substituted aralkyl, and cycloalkyl-substitutedaralkyl.

The terms “a” and “b” are independently an integer in a range of 1-10,1-8, 2-6, or 3-4. Preferably, “a” is 1 and “b” is 2. The substituent “X”may be O or NH. Preferably, X is NH.

The substituent “W” is an optionally subsituted arylene, which is asubstituent derived from an arene that has had a hydrogen atom removedfrom each of two adjacent ring carbon atoms. Exemplary arenes include anoptionally substituted benzene, naphthalene, anthracene, phenanthrene,tetracene, chrysene, triphenylene, pyrene, pentacene, benzo[a]pyrene,corannulene, benzo[ghi]perylene, coronene, ovalene, benzo[c]fluorene. Insome embodiments, the arylene is a phenylene.

The term “solvate” means a physical association of the complex of thisdisclosure with one or more solvent molecules, whether organic orinorganic. The physical association includes hydrogen bonding. Incertain instances the solvate will be capable of isolation, for examplewhen one or more solvent molecules are incorporated in the crystallattice of the crystalline solid. The solvent molecules in the solvatemay be present in a regular arrangement and/or a non-orderedarrangement. The solvate may comprise either a stoichiometric ornonstoichiometric amount of the solvent molecules. Solvate encompassesboth solution-phase and isolable solvates. Exemplary solvates include,but are not limited to, hydrates, ethanolates, methanolates, andisopropanolates. Methods of solvation are generally known in the art.

The term “stereoisomer” refers to isomers that have the same molecularformula and sequence of bonded atoms, but differ in thethree-dimensional orientations of their atoms in space.

The metal “M” is chromium, nickel, iron, lead, ruthenium, or rhodium.Preferably, M is iron. During the past few decades, ferrocene-basedcomplexes have been widely studied because their electron-rich aromaticstructural motifs can be readily functionalized by electrophilicaromatic substitution reactions. In addition, their relatively low cost,thermal stability, high tolerance to moisture and oxygen, and veryunique chemical properties make these materials attractive. Despite theimpressive progress in ferrocene-based homogeneous catalysis, the use offerrocene in heterogeneous catalysis has remained largely unexplored.

In some embodiments, the complex is:

The complex represented by Formula (IA), Formula (IB), Formula (IIA), orFormula (IIB) may be prepared by the following procedure. The complexprecursor represented by Formula (V) or Formula (VI) may be dissolved ina solvent (preferably an anhydrous solvent) and then mixed with thecompound of Formula (VII) or Formula (VIII) and a base. The complexprecursor is:

where LG is Cl, Br, I, OTf (triflate), OTs (p-toluenesulfonate), or OAc(acetate).

The compound of Formula (VII) or Formula (VIII) is:

A concentration of the precursor represented by Formula (V) or Formula(VI) in the solvent may be in a range of 10-1,000 mM, 20-500 mM, or40-100 mM. A concentration of the compound of Formula (VII) or (VIII) inthe resulting reaction mixture may be in a range of 10-1,000 mM, 50-500mM, or 100-200 mM. A concentration of the base in the resulting reactionmixture may be in a range of 0.1-2 M, 0.3-1.5 M, or 0.5-1 M. Theresulting reaction mixture may be kept under an inert atmosphereprovided by inert gases such as argon, nitrogen, or mixtures thereof.The reaction mixture may be agitated at a temperature of 30-95° C.,50-90° C., or 70-85° C. for 5-30 hours, 8-20 hours, or 10-15 hoursthereby forming the complex represented by Formula (IA), Formula (IB),Formula (IIA), or Formula (IIB). The reaction mixture may be agitatedthroughout the duration of the reaction by employing a rotary shaker, amagnetic stirrer, a centrifugal mixer, or an overhead stirrer. Inanother embodiment, the reaction mixture is left to stand (i.e. notstirred). In one embodiment, the reaction mixture is sonicated in anultrasonic bath or with an ultrasonic probe. An external heat source,such as a water bath or an oil bath, an oven, microwave, or a heatingmantle, may be employed to heat the reaction mixture. In a preferredembodiment, the external heat source is a thermostattedthermocirculator. In some embodiments, the reaction mixture is heatedwith microwave irradiation. The complex may be isolated and purified bymethods known to those skilled in the art, such as filtration through acelite containing cartridge, aqueous work-up, extraction with organicsolvents, distillation, crystallization, column chromatography, and highpressure liquid chromatography (HPLC) on normal phase or reversed phase.Preferred methods include, evaporating the reaction mixture to dryness,purifying the residue with column chromatography, and recrystallization.An isolated yield of the complex may be in a range of 30-90%, 40-80%, or50-70%.

As used herein, the term “solvent” includes, but is not limited to,water (e.g. tap water, distilled water, doubly distilled water,deionized water, deionized distilled water), organic solvents, such asethers (e.g. diethyl ether, tetrahydrofuran, 1,4-dioxane,tetrahydropyran, t-butyl methyl ether, cyclopentyl methyl ether,di-iso-propyl ether), glycol ethers (e.g. 1,2-dimethoxyethane, diglyme,triglyme), alcohols (e.g. methanol, ethanol, trifluoroethanol,n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-pentanol,i-pentanol, 2-methyl-2-butanol, 2-trifluoromethyl-2-propanol,2,3-dimethyl-2-butanol, 3-pentanol, 3-methyl-3-pentanol,2-methyl-3-pentanol, 2-methyl-2-pentanol, 2,3-dimethyl-3-pentanol,3-ethyl-3-pentanol, 2-methyl-2-hexanol, 3-hexanol, cyclopropylmethanol,cyclopropanol, cyclobutanol, cyclopentanol, cyclohexanol), aromaticsolvents (e.g. benzene, o-xylene, m-xylene, p-xylene, and mixtures ofxylenes, toluene, mesitylene, anisole, 1,2-dimethoxybenzene,α,α,α,-trifluoromethylbenzene, fluorobenzene), chlorinated solvents(e.g. chlorobenzene, dichloromethane, 1,2-dichloroethane,1,1-dichloroethane, chloroform), ester solvents (e.g. ethyl acetate,propyl acetate), amide solvents (e.g. dimethylformamide,dimethylacetamide, N-methyl-2-pyrrolidone), urea solvents, ketones (e.g.acetone, butanone), acetonitrile, propionitrile, butyronitrile,benzonitrile, dimethyl sulfoxide, ethylene carbonate, propylenecarbonate, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, andmixtures thereof.

As used herein, the term “base” includes, but is not limited to, analkali metal hydride (e.g. sodium hydride, potassium hydride), an alkalimetal hydroxide (e.g. lithium hydroxide, potassium hydroxide, sodiumhydroxide, cesium hydroxide), an alkali metal carbonate (e.g. lithiumcarbonate, potassium carbonate, sodium carbonate, cesium carbonate), analkali metal acetate (e.g. lithium acetate, sodium acetate, potassiumacetate), an amine (e.g. trialkylamine of formula NR′₃ (where each R′may be independently ethyl, n-propyl, and n-butyl) and dialkylamine offormula HNR′₂, or mixtures thereof, diethylamine, di-n-butylamine,pyrrolidine, piperidine, triethylamine, tri-n-butylamine,diisopropylethylamine, dicyclohexylmethylamine, pyridine,2,6-dimethylpyridine, 4-aminopyridine,N-methyl-2,2,6,6-tetramethylpiperidine, 2,2,6,6-tetramethylpiperidine,2,6-di-tert-butylpyridine, 1,4-diazabucyclo[2.2.2]octane), and mixturesthereof. In some embodiments, the base is ammonium hydroxide.Preferably, the base is triethylamine.

The second aspect of the disclosure relates to the functionalizedmagnetic nanoparticle comprising (i) a nanoparticle comprising amagnetic metal oxide, and (ii) a complex represented by Formula (IIIA),Formula (IIIB), Formula (IVA), or Formula (IVB), a solvate, or astereoisomer thereof:

The use of nanoparticles in catalysis is advantageous becauseperformance characteristics of homogeneous catalysts can be obtainedwithout the separation problems of homogeneous catalysts.

The nanoparticle may preferably be spherical or substantially spherical(e.g., oval or oblong shape). In other embodiments, the nanoparticle canbe of any shape that provides desired photocatalytic activity. In someembodiments, the nanoparticle is in the form of at least one shape suchas a sphere, a rod, a cylinder, a rectangle, a triangle, a pentagon, ahexagon, a prism, a disk, a platelet, a flake, a cube, a cuboid, and anurchin (e.g., a globular particle possessing a spiky uneven surface).

The nanoparticles may be uniform. As used herein, the term “uniform”refers to no more than 10%, no more than 5%, no more than 4%, no morethan 3%, no more than 2%, or no more than 1% of the distribution of thenanoparticles having a different shape. For example, the mixed metalspheres are uniform and have no more than 1% of nanoparticles in anoblong shape. In some embodiments, the nanoparticles may be non-uniform.As used herein, the term “non-uniform” refers to more than 10% of thedistribution of the nanoparticles having a different shape.

Dispersity is a measure of the heterogeneity of sizes of molecules orparticles in a mixture. In probability theory and statistics, thecoefficient of variation (CV), also known as relative standard deviation(RSD) is a standardized measure of dispersion of a probabilitydistribution. It is expressed as a percentage and is defined as theratio of the standard deviation (a) of to the mean (μ, or its absolutevalue |μ|). The CV or RSD is widely used to express precision andrepeatability. It shows the extent of variability in relation to themean of a population. The nanoparticles having a narrow size dispersion,i.e. monodispersity, is preferred. As used herein, “monodisperse”,“monodispersed” and/or “monodispersity” refers to nanoparticles having aCV or RSD of less than 25%, preferably less than 20%.

The nanoparticles may be monodisperse with a coefficient of variation orrelative standard deviation (ratio of the particle size standarddeviation to the particle size mean) of less than 15%, less than 12%,less than 10%, less than 9%, less than 8%, less than 7%, less than 6%,less than 5%, or preferably less than 2%.

In one embodiment, the nanoparticles are monodisperse and have aparticle diameter distribution in a range of 75% of the average particlediameter to 125% of the average particle diameter, 80-120%, 85-115%,86-114%, 87-113%, 88-112%, 89-111%, 90-110%, or preferably 95-105% ofthe average particle diameter.

An average diameter (e.g., average particle diameter) of thenanoparticle, as used herein, refers to the average linear distancemeasured from one point on the nanoparticle through the center of thenanoparticle to a point directly across from it. The nanoparticles mayhave an average diameter in a range of 1-20 nm, 2-18 nm, 4-15 nm, or 6-8nm. In some embodiments, the nanoparticles have an average diameter in arange of 20-100 nm, 25-70 nm, or 30-40 nm. The nanoparticles may beagglomerated or, preferably, non-agglomerated (i.e. the nanoparticlesare well separated from one another and do not form clusters). In oneembodiment, the nanoparticles are agglomerated and the agglomerates havean average diameter in a range of 10-500 nm, 50-300 nm, or 100-200 nm.The nanoparticles may be crystalline, polycrystalline, nanocrystalline,or amorphous. Preferably, the nanoparticles are nanocrystalline. Thenanoparticles may have multiple phases or a single phase. A crystallitesize may range from 1-20 nm, 5-15 nm, or 8-10 nm. The nanoparticles mayhave a microstrain in a range of 0.1-1%, 0.2-0.8%, or 0.3-0.5%. As usedherein, the term “microstrain” refers to the root mean square of thevariations in the lattice parameters across the individualnanocrystallites.

The nanoparticles may have a BET surface area in a range of 50-2,000m²/g, 200-1,600 m²/g, or 500-1,400 m²/g. The BET surface area may bedetermined by physical adsorption of a gas on the surface of thenanoparticles and then calculating the amount of adsorbate gascorresponding to a monomolecular layer on the surface.

The dimensions and the characteristics of the nanoparticles may varyfrom the described ranges and the functionalized magnetic nanoparticlecan still function as intended.

The magnetic metal oxide may be at least one metal oxide selected fromthe group consisting of nickel(II) oxide, chromium(IV) oxide,manganese(II) oxide, manganese(III) oxide, iron(II) oxide, and iron(III)oxide. In some embodiments, the magnetic metal oxide is manganese(II)oxide and manganese(III) oxide, or manganese(II,III) oxide, Mn₃O₄.Preferably, the magnetic metal oxide is iron(II) oxide and iron(III)oxide. In some embodiments, the magnetic metal oxide is iron(II,III)oxide, Fe₃O₄. In some embodiments, the magnetic metal oxide isferrimagnetic containing populations of atoms with opposing magneticmoments. However, the opposing moments are unequal and a spontaneousmagnetization remains. In preferred embodiments, the magnetic metaloxide shows superparamagnetism which is a form of magnetism appearing inferromagnetic or ferrimagnetic nanoparticles. In sufficiently smallnanoparticles, such as the nanoparticles described herein, magnetizationcan randomly flip direction under the influence of temperature. In theabsence of an external magnetic field, the magnetization appears to bezero and the nanoparticles are in the superparamagnetic state. In thisstate, an external magnetic field is able to magnetize thenanoparticles. Superparamagnetic nanoparticles have a magneticsusceptibility larger than that of paramagnets. The chemical andphysical properties (i.e., shape, size, and morphology) ofsuperparamagnetic iron oxide nanoparticles (SPION) can easily bemanipulated. The synthesis of SPION is straightforward and thenanoparticles are easily functionalized (C. O. Dalaigh, S. A. Corr, Y.Gunko, S. J. Connon, Angew. Chem. Int. Ed. 46 (2007) 4329-4332,incorporated herein by reference in its entirety).

The presence of the magnetic metal oxide provides for an easy recoveryof the functionalized magnetic nanoparticle and the catalyst of thepresent disclosure. For example, the functionalized magneticnanoparticle or catalyst is insoluble in solvents and can be easilyseparated from other components of the reaction mixture by attractingthe functionalized magnetic nanoparticle or the catalyst with a magnet.

The magnetic metal oxide may have a saturation magnetization in a rangeof 5-150 emu/g, 30-100 emu/g, or 50-70 emu/g. The magneticsusceptibilities may be measured with a laboratory magnetometer such asa vibrating sample magnetometer, a superconducting quantum interferencedevice, inductive pickup coils, a pulsed field extraction magnetometer,a torque magnetometer, a faraday force magnetometer, and an opticalmagnetometer. The magnetic metal oxide may have a coercivity (Hc) in arange of 3-4 Oe, 3.3-3.99 Oe, or 3.8-3.97 Oe. As used herein, the term“coercivity” refers to the resistance of a magnetic material to changesin magnetization, and is equivalent to the field intensity necessary todemagnetize the fully magnetized material. The magnetic metal oxide mayhave a remanence (Mr) in a range of 0.75-2 emu/g, 0.8-1.5 emu/g or 0.8-1emu/g. As used here, the term “remanence” refers to the magnetizationleft behind in the magnetic metal oxide after an external magnetic fieldis removed. Remanence is also the measure of that residualmagnetization.

The magnetic metal oxide may be purchased or made in-house. The magneticmetal oxide may be produced by the following procedure. A metal salt maybe mixed with an alkaline solution at 20-30° C., 22-28° C., 24-26° C.under an inert atmosphere. Exemplary metal salts include, halides (e.g.,fluoride, chloride, bromide, and iodide), nitrates, acetylacetonates,acetates, perchlorates, sulfamates, trifluoroacetylacetonates,carbonates, bicarbonates, methanesulfonates, ethanesulfonates,p-toluenesulfonates, salicylates, malates, maleates, succinates,tartrates, citrates, trifluoromethanesulfonates (triflates),hexafluorophosphates, hexafluoroacetylacetonates, sulfites, phosphate,and sulfates of chromium, nickel, iron, lead, ruthenium, and rhodium. Inmost embodiments, the metal salt is a hydrate. The alkaline solution mayhave a pH in a range of 8-14, 9-13, or 10-12, and comprises any of theaforementioned base. Preferably, the base is ammonium hydroxide. Thereaction mixture may be agitated with the aforementioned method for1-10, 2-8 hours, or 4-6 hours. Preferably, the reaction mixture isstirred. The pH of the solution may be maintained with the periodicaddition (e.g., every 30-100 minutes, every 40-70 minutes, or every50-60 minutes) of the base. The magnetic metal oxide formed may beinsoluble in the alkaline solution and may be collected with a magnetand washed with water several times to remove any unreacted metal saltprecursors.

In some embodiments, the magnetic metal oxide is Mn₃O₄ and/or Fe₃O₄, andthe magnetic metal oxide may be prepared by mixing the respectivedivalent and trivalent metal salts in a stoichiometric ratio of 1:2, or0.8:2 to 1.2:2, 0.9:2 to 1.1:2, or 0.95:2 to 1.05:2. In someembodiments, the divalent metal salt may be in slight excess, forexample, not more than 10 mol %, not more than 5 mol %, not more than 3mol %, relative to the stoichiometric amount of the trivalent metalsalt. In some embodiments, the trivalent metal salt may be in slightexcess, for example, not more than 10 mol %, not more than 5 mol %, notmore than 3 mol %, relative to the stoichiometric amount of the divalentmetal salt.

The functionalized magnetic nanoparticle may be prepared by thefollowing procedure. The complex of Formula (IA), Formula (IB), Formula(IIA), or Formula (IIB) may be dissolved in the aforementioned solvent(preferably an anhydrous organic solvent). Preferably, the solvent ischloroform. A concentration of the complex solution may be in a range of1-1,000 mM, 2-500 mM, or 5-100 mM. The nanoparticles may be suspended inthe same or different solvent. Preferably, the solvent is methanol. Anamount of the nanoparticles in the suspension may be in a range of 1-500mg/ml of solvent, 10-300 mg/ml, or 100-200 mg/ml. The complex solutionmay be mixed with the suspension of the nanoparticles under an inertatmosphere. The resulting reaction mixture may be agitated with theaforementioned methods of agitation for 0.5-20 hours, 1-15 hours, or5-10 hours thereby forming the functionalized magnetic nanoparticles. Ina preferred embodiment, the reaction mixture is sonicated at a range of20-120 kHz, 30-90 kHz, or 40-80 kHz. In some embodiments, the sonicationduration is about 3-20 min, about 5-15 min, or about 8-12 min. Thefunctionalized magnetic nanoparticles may be collected with a magnet.The complex of Formula (IIIA), Formula (IIIB), Formula (IVA), or Formula(IVB) may be dispersed throughout the functionalized magneticnanoparticle, and may be determined by EDX spectrum and elemental maps.The unreacted complex may be removed from the functionalized magneticnanoparticles by washing the functionalized magnetic nanoparticles withthe solvent.

The complex of Formula (IIIA), Formula (IIIB), Formula (IVA), or Formula(IVB) is bound to a surface of the nanoparticle through an oxygen atomin the —OR⁹ group in a monodentate or bidentate manner via a covalentbond (e.g., non-ionic dative bond), an ionic bond, or van der Waalsforce. The binding of an oxygen atom in the —OR⁹ group may stabilize andminimize aggregation of the functionalized magnetic nanoparticles (C.Duanmu, L. Wu, J. Gu, X. Xu, L. Feng, X. Gu, Catal. Commun. 48 (2014)45-49, incorporated herein by reference in its entirety). In someembodiments, R⁹ is a single bond and/or R^(9′) is —O—, the oxygen atomis covalently bonded to the surface of the nanoparticle. In alternativeembodiments, the —OR⁹ group may be replaced with a —NR⁵ ₂ group and thefunctionalized magnetic nanoparticle will still function as intended (F.Zhang, J. Jin, X. Zhong, S. Li, J. Niu, R. Li, J. Ma, Green Chem. 13(2011) 1238-1243; T. Jiang, S. Du, T. Jafari, W. Zhong, Y. Sun, W. Song,Z. Luo, W. A. Hines, S. L. Suib Applied Catalysis A: General 502 (2015)105-113; B. Baruwati, D. Guin, S. V. Manorama, Org. Lett. 9 (2007)5377-5380; and V. Polshettiwar, R. S. Varma, Org. Biomol. Chem. 7 (2009)37-40, each incorporated herein by reference in their entirety).

The functionalized magnetic nanoparticle may have a saturationmagnetization in a range of 5-150 emu/g, 30-100 emu/g, or 40-70 emu/g.The loading of the complex of Formula (IIIA), Formula (IIIB), Formula(IVA), or Formula (IVB) on the surface of the nanoparticle is in a rangeof 0.01-10 mmol/g of the nanoparticles, 0.05-1 mmol/g, or 0.2-0.5mmol/g. The loading may be determined from thermogravimetry.

The catalyst may be prepared by the following procedure. Thefunctionalized magnetic nanoparticles may be suspended in theaforementioned solvent and agitated with the aforementioned method for1-120 mins, 10-100 minutes, or 20-70 minutes. Preferably, the solvent ischloroform. An amount of the functionalized magnetic nanoparticles inthe solvent may be in a range of 1-500 mg/ml of solvent, 10-300 mg/ml,or 50-200 mg/ml. The metal precursor may be dissolved in the same ordifferent solvent. Preferably, the solvent is dichloromethane.

The metal precursor may be a binuclear metal complex, a mononuclearmetal complex, or a metal salt of ruthenium, iridium, palladium, orrhodium. Exemplary metal precursors include, without limitation,allylpalladium(II) chloride dimer, (2-methylallyl)palladium(II) chloridedimer, palladium(π-cinnamyl) chloride dimer, (2-butenyl)chloropalladiumdimer, palladium(II) chloride, palladium(II) bromide, palladium(II)iodide, bis(benzonitrile) palladium(II) chloride,bis(acetonitrile)palladium(II) chloride, palladium(II) acetate,dichloro(mesitylene)ruthenium(II) dimer,bis(2-methylallyl)(1,5-cyclooctadiene)ruthenium(II),bis(1,5-cyclooctadiene)iridium(I) tetrafluoroborate,bis(1,5-cyclooctadiene)diiridium(I) dichloride,bicyclo[2.2.1]hepta-2,5-diene-rhodium(I) chloride dimer,chloro(1,5-cyclooctadiene)rhodium(I) dimer,hydroxy(cyclooctadiene)rhodium(I) dimer,chlorobis(cyclooctene)rhodium(I) dimer,methoxy(cyclooctadiene)rhodium(I) dimer, chloro(1,5-hexadiene)rhodium(I)dimer, bis(1,5-cyclooctadiene)rhodium(I) tetrafluoroborate,bis(1,5-cyclooctadiene)rhodium(I)tetrakis[bis(3,5-trifluoromethyl)phenyl]borate,bis(acetonitrile)(1,5-cyclooctadiene)rhodium(I)tetrafluoroborate,bis(1,5-cyclooctadiene)rhodium(I) hexafluoroantimonate, andbis(norbornadiene)rhodium(I) trifluoromethanesulfonate.

A concentration of the metal precursor may be in a range of 0.01-100 mM,0.05-50 mM, or 0.1-10 mM. A molar ratio of the metal precursor to thebound complex of Formula (IIIA), Formula (IIIB), Formula (IVA), orFormula (IVB) may be in a range of 1:1 to 2:1, 1.1:1 to 1.9:1, or 1.3:1to 1.5:1. The solution of the metal precursor may then be added to thesuspension of the functionalized magnetic nanoparticles and agitated bythe aforementioned method for 0.5-10 hours, 1-8 hours, or 3-6 hoursunder an inert atmosphere. The catalyst may be collected with magnet andwashed with the solvent to removed unreacted metal precursor.

The catalyst comprises palladium, rhodium, iridium, or ruthenium boundto a phosphorous atom in at least one —PR⁸ ₂ group in the complex ofFormula (IIIA), Formula (IIIB), Formula (IVA), or Formula (IVB). Thefunctionalized nanoparticle may bind to the palladium, rhodium, iridium,or ruthenium in a monodentate manner via a covalent bond (preferably anon-ionic dative bond) through a phosphorous atom in one —PR⁸ ₂ group,or in a bidentate manner via a covalent bond (preferably a non-ionicdative bond) through a phosphorous atom in both —PR⁸ ₂ groups.

The catalyst may have a saturation magnetization in a range of 5-150emu/g, 30-100 emu/g, 30-70 emu/g, or 30-60 emu/g. The catalyst may havea turnover number in a range of 1,500-2,500, preferably 1,500-2,000,more preferably 1,700-2,000 and a turnover frequency in a range of200-1,500 per hour, preferably 200-1,000 per hour, more preferably200-500 per hour. Preferably, the catalyst tolerates a variety offunctional groups on the reactants. That is, the catalyst maintains theaforementioned turnover number and turnover frequency regardless of thefunctional groups on the reactants.

The catalyst may be useful for reactions such as Mizoroki-Heck reaction,Mizoroki-Heck-Matsuda, Sonogashira, Kumada, Negishi, Stille, Suzuki,Hiyama, Buchwald-Hartwig, hydroformylation, hydrogenation, allylicalkylation, Michael addition, cyciopropanation, hydroboration, olefinisomerization and hydroacylation, hydrosilylation and silylformylation,cycloisomerization and cyclotrimerization, Alder-ene, allylicsubstitution, carbocyclizations, carbon-hydrogen insertion, oxidativeamination, ylide rearrangements, and 1,3-dipolar cycloadditions.Preferably, it catalyzes reactions such as a hydroformylation reactionand a Heck reaction.

In some embodiments, the catalyst is not preformed but is formed in situin a reaction flask (i.e., at least one of the aforementioned metalprecursors and the functionalized magnetic nanoparticles are added tothe reaction flask separately).

In some embodiments, the catalyst comprises rhodium, ruthenium, oriridium bound to a phosphorous atom in at least one —PR⁸ ₂ group and thecatalyst catalyzes the hydroformylation reaction. Preferably, thecatalyst comprises rhodium bound to a phosphorous atom in at least one—PR⁸ ₂ group. In a hydroformylation reaction, an optionally substitutedalkene is mixed with carbon monoxide and hydrogen gases in the presenceof the catalyst and optionally a solvent thereby forming an aldehyde.The aldehyde may be a linear or branched aldehyde. Prior to the mixingwith carbon monoxide and hydrogen gases, the optionally substitutedalkene and the catalyst may be mixed under an inert atmosphere in thereaction vessel and the mixture is optionally agitated. After which, thereaction vessel is purged with the carbon monoxide and hydrogen gasesfor 1-10 times, 2-8 times, or 3-6 times. A molar ratio of the carbonmonoxide gas to the hydrogen gas may be in a range of 1:3 to 3:1, 1:2 to2:1, about 1:1. Preferably, syngas is used. The carbon monoxide gas maybe replaced by aldehydes, higher alcohols (e.g., cinnamyl alcohol,polyols), and metal carbonyls (e.g., Mo(CO)₆ and W(CO)₆) to reduce theuse of toxic and flammable carbon monoxide gas, and the hydroformylationmay still proceed as intended. The reacting may be carried out at apressure in a range of 100-2,000 psi, 200-1,500 psi, or 500-1,000 psifor 5-20 hours, 8-16 hours, or 10-14 hours at a temperature in a rangeof 30-90° C., 40-80° C., or 45-70° C. under an inert atmosphere. Thereaction mixture may be optionally agitated. The progress of eachreaction may be monitored by methods known to those skilled in the art,such as thin layer chromatography, gas chromatography, nuclear magneticresonance, infrared spectroscopy, and high pressure liquidchromatography combined with ultraviolet detection or mass spectroscopy.Preferably, gas chromatography combined with mass spectroscopy is used.

The conversion of the optionally substituted alkene to the aldehyde maybe more than 80%, more than 90%, more than 95%, or more than 99%, basedon the number of moles of the optionally substituted alkene. Thealdehyde may be linear or branched (see Table 3 for examples of linearand branched aldehydes). In most embodiments, the hydrogenatedby-product was not observed in the reaction mixture. For example, theremay be less than 0.1 wt %, less than 0.05 wt %, or less than 0.01 wt %of the hydrogenated by-product.

The optionally substituted alkene may be an optionally substituted vinylarene (e.g., styrene, 4-methyistyrene, 4-vinylanisole, 4-chlorostyrene,3-nitrostyrene, 2-bromostyrene, and vinylbenzoate) or n-alkene (e.g.,1-octene). An amount of the optionally substituted alkene may be in arange of 0.1-50 mmol, 0.5-20 mmol, or 1-10 mmol. In some embodiments,the optionally substituted alkene may be substituted withelectron-donating groups such as amino, amido, hydroxy, alkoxyl, andalkyl. In other embodiments, the optionally substituted alkene issubstituted with electron-withdrawing groups such as nitro, cyano, andacetyl. Electron-withdrawing substituents are preferred because thebranched aldehydes are formed in high yields (more than 90%, more than95%, or more than 98%).

In some embodiments, the optionally substituted alkene is a substitutedstyrene, and the aryl group may comprise up to 5 substituents.Preferably, there is one substituent. The substituent may be locatedortho, meta, or para to the vinyl group. Preferably, the substituent islocated para to the vinyl group.

The amount of catalyst may be in a range of 0.1-30 mol %, 0.5-20 mol %,or 1-10 mol %, based on the number of moles of the optionallysubstituted alkene. Higher catalyst loadings (e.g. up to 20 mol %, 30mol %, 40 mol %, 80 mol %) may be used and the method will still proceedas intended.

In some embodiments, the solvent is present and may be DCM, THF, ormixtures thereof. In these embodiments, a concentration of theoptionally substituted alkene is in a range of 10-1,000 mM, 50-500 mM,or 100-300 mM. The polarity of the solvent affects the regioselectivityof the hydroformylation reaction and thus non-polar solvents arepreferably used to obtain the branched aldehyde in high yields. A weightratio of the branched aldehyde to the linear aldehyde may be in a rangeof 200:1 to 1:200, 100:1 to 1:100, or 100:1 to 1:1. The selectivitytoward the branched aldehyde may be due to: (1) the catalytic metalbinding sites being far away from the metal nanoparticle surface andthus are not hindered by the nanoparticles; and (2) the stericenvironment around the phosphines coordinated to the catalytic metalresulted in the predominant production of one isomer.

In some embodiments, the optionally substituted alkene is an n-alkene,and the weight ratio of the branched aldehyde to the linear aldehyde isin a range of 1:50 to 1:150, 1:80 to 1:120, or 1:100 to 1:110.

In some embodiments, the catalyst comprises palladium bound to aphosphorous atom in at least one —PR⁸ ₂ group and the catalyst catalyzesthe Mizoroki-Heck coupling reaction. In a Mizoroki-Heck couplingreaction, an optionally substituted styrene (e.g., styrene,4-methylstyrene, 4-vinylanisole, 4-chlorostyrene, 3-nitrostyrene,2-bromostyrene) reacts with an aryl halide in the presence of thecatalyst, the aforementioned solvent, and the aforementioned basethereby forming a coupling product. The reaction may be carried out at atemperature in a range of 50-100° C., 60-95° C., or 70-90° C., for 10minutes to 30 hours, 30 minutes to 24 hours, or 60 minutes to 4 hours.The reaction may be carried out in an inert atmosphere or in air. Thereaction mixture may be optionally agitated.

Preferably, the aryl halide is bromobenzene or iodobenzene. In otherembodiments, a benzyl halide, a vinyl halide, an aryl triflate, a benzyltriflate, a vinyl triflate, an aryl tosylate, a benzyl tosylate, or avinyl tosylate may be used in place of the aryl halide.

Exemplary halides, triflates, and tosylates include, without limitation,1-bromonaphthalene, 2-bromonaphthalene, bromobenzene, 4-bromoanisole,4-bromotoluene, 1-bromo-4-fluorobenzene, 2-bromoanisole,N-methyl-2-bromopyrrole, 3-bromoindole,5-bromo-2-methyl-1,3-benzothiazole, 3-bromobenzofuran,3-bromobenzothiophene, 2-bromothiophene, 2-bromothiophene,4-bromo-3-chromene, 1-bromostyrene, (E)-2-bromostyrene,1-bromocyclohexene, 1-bromocyclopentene, bromoethene,(E)-1-bromopropene, 2-bromopropene, iodobenzene, 1-iodonaphthalene,2-iodonaphthalene, 4-iodoanisole, 4-iodotoluene, 4-chlorotoluene,2-chlorotoluene, 1-chloronaphthalene, 2-chloronaphthalene,chlorobenzene, 4-chloroanisole, 2-chloroanisole, 3-chloroindole,N-methyl-2-chloropyrrole, 5-chloro-1,3-benzothiazole,3-chlorobenzofuran, 3-chlorobenzothiophene, 2-chlorothiophene,2-chlorothiophene, phenyl tosylate, allyl tosylate, 1-naphthyl tosylate,2-naphthyl tosylate, phenyl tosylate, p-(ethoxycarbonyl)phenyl tosylate,p-anisyl tosylate, p-tert-butylphenyl tosylate, o-methylphenyl tosylate,o-anisyl tosylate, p-chlorophenyl tosylate, parabenzophenonyl tosylate,p-formylphenyl tosylate, 2-methylcyclohexenyl tosylate,2-methylbenzo[d]thiazol-5-yl tosylate, 1-tosyl-1H-indol-5-yl tosylate,m-anisyl tosylate, p-(trifluoromethyl)phenyl tosylate, andp-fluorophenyl tosylate, 1-naphthyl triflate, 2-naphthyl triflate,phenyl triflate, p-(ethoxycarbonyl)phenyl triflate, p-anisyl triflate,p-tert-butylphenyl triflate, o-methylphenyl triflate, o-anisyl triflate,p-chlorophenyl triflate, parabenzophenonyl triflate, p-formylphenyltriflate, 2-methylcyclohexenyl triflate, 2-methylbenzo[d]thiazol-5-yltriflate, 1-tosyl-1H-indol-5-yl triflate, m-anisyl triflate,p-(trifluoromethyl)phenyl triflate, and p-fluorophenyl triflate,2-thienyl and 3-thienyl triflates and their benzoderivatives, 2-furanyland 3-furanyl triflates and their benzoderivatives, N-Boc-2-pyrrolidinyland N-Boc-3-pyrrolidinyl triflates, cyclohexenyl triflate, 1-styryl and(E)-2-styryl triflates. Other traditional Heck cross-coupling partners(e.g. mesylates) and non-traditional Heck cross-coupling partners (e.g.alkyl halides, triflates, tosylates, etc.) are known to those ofordinary skill and may also be suitable reaction partners in thedisclosed method.

The aryl halide comprises an optionally substituted aryl group which maycomprise the aforementioned substituents. Preferably, the aryl group isphenyl. In a preferred embodiment, the substituents areelectron-donating groups such as amino, alkoxyl, and alkyl. In anotherpreferred embodiment, the substituents are electron-withdrawing groupssuch as nitro, cyano, and acetyl. The aryl group may comprise up to 5substituents. Preferably, there is one substituent. The substituent maybe located ortho, meta, or para to the halogen atom. Preferably, thesubstituent is located para to the halogen atom.

The aryl halide may be an aryl monohalide such as aryl chloride, arylbromide, and aryl iodide. Preferably, the aryl monohalide is an aryliodide such as iodobenzene. Exemplary aryl monohalide includes, withoutlimitation, iodobenzene, 4-iodoaniline, 4-iodoacetophenone,4-iodobenzonitrile, 4-iodoanisole, bromobenzene, 4-bromoacetophenone,and 1-iodo-4-nitrobenzene. In another embodiment, the aryl halide is anaryl dihalide such as 1,4-dichlorobenzene, 1,4-dibromobenzene, and1,4-diiodobenzene.

The aforementioned base may be used in the Mizoroki-Heck reaction.Preferably the base is potassium hydroxide. The presence of a base isoften important for the palladium-catalyzed Mizoroki-Heck couplingreaction in order to neutralize the hydrogen halide produced as theby-product of the coupling reaction (Chih-chung, T.; Mungyuen, L.;Bingli, M.; Sarah, W.; Alan, S. C.; Chem. Lett. 2011, 40:9 955.Thorwirth, R.; Stolle, A.; Ondruschka, B.; Green Chem. 2010, 12, 985.Bakherad, M.; Keivanloo, A.; Samangooei, S.; Omidian, M. J. Organometal.Chem. 2013, 740, 78. Feng, Z.; Yu, S.; Shang, Y. Appl. Organometal.Chem. 2008, 22, 577. Shingo, A.; Motohiro, S.; Yuki, S.; Hirojiki, S.;Takuya, Y.; Aiky, O. Chem. Lett. 2011, 40:9, 925. Korzec, M.; Bartczak,P.; Niemczyk, A.; Szade, J.; Kapkowski, M.; Zenderowska, P.; Balin, K.;Lelarko, J.; Polariski, J. J. Catal, 2014, 313, 1. Zhang, G.; Luan, Y.;Han, X.; Wang, Y.; Wen, X.; Ding, C. Appl. Organometal. Chem. 2014, 28,332, each incorporated herein by reference in their entirety).

A concentration of the optionally substituted styrene may be in a rangeof 10-1,000 mM, 50-500 mM, or 100-300 mM. A concentration of the base inthe reaction mixture may be in a range of 10-1,000 mM, 50-500 mM, or100-300 mM. A concentration of the aryl halide in the reaction mixturemay be in a range of 5-1,000 mM, 50-500 mM, or 100-300 mM. The arylhalide may be the limiting reagent. The amount of the optionallysubstituted styrene may be more than 1 molar equivalent, more than 1.5molar equivalents, and up to 5 molar equivalents, up to 3 molarequivalents, or up to 2 molar equivalents of the amount of aryl halide.

A molar ratio of the base to the optionally substituted styrene may bein range of 10:1 to 1:10, 5:1 to 1:5, 2:1 to 1:2, or about 1:1.

The amount of catalyst may be in a range of 0.1-30 mol %, 0.5-20 mol %,or 1-10 mol %, based on the number of moles of the aryl halide. Highercatalyst loadings (e.g. up to 20 mol %, 30 mol %, 40 mol %, 80 mol %)may be used and the method will still proceed as intended.

The aforementioned solvent may be used in the Mizoroki-Heck couplingreaction. Preferably, the solvent comprises at least one selected fromthe group consisting of DMF, water, and toluene. Preferably, the solventis a mixture consisting of dimethyl formamide and water and contains10-50 vol %, preferably 30-50 vol %, more preferably 40-50 vol % ofwater, based on a total volume of the solvent.

In some embodiments, the solvent is water and a surfactant (e.g., sodiumdodecylsulfate, TWEEN®, and PLURONICS™) may be present to dissolve theorganic reactants and facilitate their interaction with the catalyst.

The reaction may be monitored by gas chromatography which is optionallycoupled to a mass spectrometer. The yield of the reaction may be morethan 40%, more than 60%, more than 80%, or more than 95%. In mostembodiments, the biphenyl by-product was not observed in the reactionmixture. For example, there may be less than 0.1 wt %, less than 0.05 wt%, or less than 0.01 wt % of the biphenyl by-product.

The products obtained by the catalyzed methods of the present disclosureare isolated and purified by employing the aforementioned methods whichare well-known to those skilled in the art. The products, resultingeither from a single run or a combination of runs, comprises less than10 ppb iron, and/or palladium, rhodium, ruthenium, or iridium, (measuredby ICP-MS), preferably less than 5 ppb, more preferably less than 1 ppb,based on a total weight of the product. The leaching of the catalyticmetal from the catalyst of the present disclosure into the products isminimal and thus the catalyst may be recycled and reused without muchloss in the catalytic activity.

The reaction mixture is preferably heterogeneous and comprises suspendedcatalyst particles in the liquid reaction mixture. In one embodiment,the catalyst particles are dispersed within the reaction mixture, andmay further be filtered and recycled at the end of the reaction. In oneembodiment, the catalyst is placed in a bag and the bag is immersed inthe reaction mixture. Accordingly, the catalyst remains in the bag untilthe catalyzed reaction is completed.

In some embodiments, the method further comprises separating thecatalyst from the products, followed by recycling the used catalyst. Thecatalyst may be separated by removing the bag of catalyst, dialysis in asolvent, or using a micro-filter or a paper filter. Preferably, thecatalyst is separated from the products by attracting the catalyst witha magnet placed at the bottom of the exterior of the reaction vessel andthen decanting the reaction mixture.

The phrase “recycling the catalyst” refers to a process whereby thecatalyst is washed by an organic solvent, dried, and then added to a newbatch of reactants (either for the same or a different type of catalyzedreaction). Preferred organic solvents for washing the catalyst and/ordialysis may include, without limitation, methanol, acetone, ethanol,tetrahydrofuran, acetonitrile, dichloromethane, ether, glycol ether,acetamide, dimethyl acetamide, dimethyl sulfoxide, water, orcombinations thereof. The catalyst may be dried in vacuum (e.g., in apressure of 0.01-100 mbar, 0.1-50 mbar, or 1-10 mbar), and/or withheating, for example, the catalyst may be dried in a vacuum oven. Driedcatalyst may be stored in a desiccator until the next run.

In one embodiment, the catalyst is recycled for at least 2 runs,preferably at least 10 runs, more preferably at least 20 runs, even morepreferably at least 30 runs. In some embodiments, the catalyst may beused continuously for 10-50 days, 20-40 days, or 28-32 days. Thecatalyst may lose less than 5 wt %, preferably less than 2 wt %, morepreferably less than 0.1 wt % of palladium/rhodium/iridium/ruthenium(based on an initial amount of palladium/rhodium/iridium/rutheniumpresent in the catalyst) after the catalyst is used for several runs orseveral days. The yield of the catalyzed reaction may decrease less than20 percentage points, less than 10 percentage points, or 5 percentagepoints after the catalyst is used for several runs or several days.Preferably, the yield of the catalyzed reaction decreases 4-8 percentagepoints after the catalyst is used for 8-12 runs or 29-31 days. Theturnover number and the turnover frequency of the catalyst may decreaseless than 10%, preferably less than 5%, more preferably less than 2%after the catalyst is used for several runs or several days.

Having generally described this disclosure, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified. The examples were published in anarticle “Magnetic nanoparticle-supported ferrocenylphosphine: a reusablecatalyst for hydroformylation of alkene and Mizoroki-Heck olefination”by M. Nasiruzzaman Shaikh, Md. Abdul Aziz, Aasif Helal, MohamedBououdina, Zain H. Yamania, and Tae-Jeong Kim, in RSC Advances, 2016,pages 41687-41695, which is incorporated herein by reference in itsentirety.

Example 1 Experimental Materials and Methods

All of the chemicals were purchased from Sigma-Aldrich and used asreceived unless otherwise stated. An inert atmosphere and standardSchlenk techniques were used wherever needed. Standard procedures werefollowed for preparing dry and deoxygenated solvents. Deionized (DI)water was used throughout the experiments. The surface coating wascarried out in a low-power bath sonicator (Cole-Parmer model 08892-21).The ¹H and ¹³C NMR spectra were recorded on a JEOL JNM-LA 500spectrometer with tetramethylsilane (TMS) as the internal standard. The³¹P NMR spectra were recorded on the same spectrometer using aphosphorous probe and 85% H₃PO₄ as the internal reference. The FTIRspectra were obtained on a Nicolet 720 in the range of 400 to 4000 cm⁻¹using KBr pellet. The thermogravimetric analysis (TGA) data wereobtained on a Mettler-Toledo model TGA1 STAR^(e) System at a heatingrate of 10° C./min in a temperature range of 25-600° C. in an argonatmosphere. The X-ray diffraction data were collected on a Rigaku modelUltima-IV diffractometer using Cu-Kα radiation. The nanoparticles wereimaged by field emission scanning electron microscopy (FESEM) on a LYRA3 Dual Beam Tescan operated at 30 kV. The SEM samples were prepared fromethanolic suspensions on alumina stabs and coated with gold in anautomatic gold coater (Quorum, Q150T E). For the elemental analysis andmapping, the energy dispersive X-ray spectra (EDS) were collected on theLYRA 3 Dual Beam Tescan. The transmission electron micrographs werecollected on a transmission electron microscope (TEM) (JEOL, JEM 2011)operated at 200 kV with a 4 k×4 k CCD camera (Ultra Scan 400SP, Gatan).The TEM samples were prepared by dropwise application of an ethanolicsuspension onto a copper grid and the sample was allowed to dry at roomtemperature. The catalytic reactions were performed in a STEM Omni®10-place reaction station and a Teflon-lined autoclave from HiTech, USA(model: M010SSG0010-E129A-00022-1D1101), which was equipped with apressure gauge and mechanical stirrer. The magnetic susceptibilitieswere measured using a vibrating sample magnetometer (VSM, model PMCMicromag 3900) equipped with a 1 tesla magnet at room temperature.

Example 2 Syntheses of the Compounds, Complex, Functionalized MagneticNanoparticle, and Catalyst

The syntheses of N,N-dimethylferrocenyl ethyl amine (FA),N,N-dimethyl-1-[1′,2-bis (diphenylphosphino)ferrocenyl]ethyl amine(BPPFA) and 1-[-1′,2-bis(diphenylphosphino)ferrocenyl]ethyl acetate(BPPFA-OAc) were performed according to previously reported procedures(G.-H. Hwang, E.-S. Ryu, D.-K. Park, S. C. Shim, C. S. Cho, T.-J. Kim,J. H. Jeong, M. Cheong, Organometallics 20 (2001) 5784-5787; and T.Hayashi, T. Mise, M. Fukushima, M. Kagotani, N. Nagashima, Y. Hamada, A.Matsumoto, S. Kawakami, M. Konishi, Bull. Chem. Soc. Japan 53 (1980)1138-1151, each incorporated herein by reference in their entirety).

The synthesis involved the preparation ofN,N-dimethyl-1-ferrocenylethylamine followed by dilithiation andreaction with chlorodiphenylphosphine to afford BPPFA (see FIG. 6) (T.Hayashi, K. Yamamoto, M. Kumada, Tetrahedron Lett. (1974) 4405-4408,incorporated herein by reference in its entirety). The freshly preparedBPPFA was acetylated to replace the —NMe₂ functional group by reactionwith acetic anhydride at 100° C. for 1 hour to yield BPPFA-OAc.

The synthesis of a new ferrocene-based ligand (dop-BPPF,{η⁵-C₅H₄-PPh₂}Fe{η⁵-C₅H₃-1-PPh₂-2-CH(Me)NH—CH₂—CH₂-4-C₆H₃-1,2-OH}) fromBPPFA-OAc (1-[1′,2-bis(diphenylphosphino)-ferrocenyl]ethyl acetate) isdescribed hereinafter (M. N. Shaikh, M. Bououdina, A. A. Jimoh, M. A.Aziz, A. Helal, A. S. Hakeem, Z. H. Yamani, T.-J. Kim, New J. Chem. 39(2015) 7293-7299; M. N. Shaikh., V. D. M. Hoang, T-J. Kim, Bull. KoreanChem. Soc. 30 (2009) 3075-3078; and H.-K. Kim, J.-A. Park, K. M. Kim, M.N. Shaikh, D.-S. Kang, J. Lee, Y. Chang, T.-J. Kim, Chem. Commun. 46(2010) 8442-8444, each incorporated herein by reference in theirentirety). Ferrocenylphosphine was used because the phosphine group cancoordinate to the catalytic metal (i.e., rhodium or palladium) and theresulting catalyst was found to be stable with excellent catalyticactivity. FIG. 1 shows the preparation route for the formation ofdopamine-functionalized ferrocenylphosphine.

Synthesis of{η⁵-C₃H₄-PPh₂}Fe{η⁵-C₅H₃-1-PPh₂-2-CH(Me(NH—CH₂—CH₂-4-Ph-1,2-OH}(dop-BPPF): To a solution of BPPFA-OAc (0.28 g, 0.43 mmol) in anhydrousmethanol (10 mL), dopamine hydrochloride (0.19 g, 1.0 mmol) and freshlydistilled triethylamine (1 mL) were added under an argon atmosphere(dopamine hydrochloride was made soluble in anhydrous methanol by theexcess trimethylamine). The mixture was stirred at 85° C. for 12 hours,and then the solvent was removed under vacuum. The solid residue wasdissolved in a minimal amount of methanol and transferred to a silicagel column for separation. The desired orange band was eluted using acombination of ethyl acetate and methanol (9:1) to produce orange solidsafter removal of the solvents. Recrystallization frommethanol/cyclohexane yielded 0.18 g of product (56%). ³¹P NMR (202 MHz,in DMSO-d₆): δ −28.14 (s, PPh₂), −20.78 (s, PPh₂). ¹H NMR (DMSO-d₆): δ1.30 (d, J=6.7, 3H, CHCH₃), 1.78 (t, 2H, NCH₂CH₂), 2.29 (t, 2H,NCH₂CH₂), 3.55 (m, 3H, C₅H₃), 4.04-4.49 (m, 4H, C₅H₄), 6.20 (d, 1H,C₆H₃), 6.39 (s, 1H, C₆H₃), 6.60 (d, 1H, C₆H₃), 7.24-7.50 (m, 20H, PPh₂),8.62 (s, 1H, OH), 8.74 (s, 1H, OH). ¹³C NMR (DMSO-d₆): 19.03 (CHCH₃),35.12 (NCH₂CH₂), 69.37 (NCH₂CH₂), 72.81 (CHCH₃), 115.29, 118.91, 128.20,129.23, 132.11 (C₆H₃), 132.67, 132.82, 133.04, 134.43, 143.20, 144.81(C₅H₃, C₅H₄ and PPh₂). FTIR in KBr (cm⁻¹): v=3426 (O—H), 3058 (arC—H),2920 (Csp³-H) 1522 (arC—C). FAB-MS (m/z): calc. for C₄₄H₄₁FeNO₂P₂,733.198 ([M]⁺); found, 733.196. Anal. Calcd for C₄₄H₄₁FeNO₂P₂.CH₃OH: C,70.59; H, 5.92; N, 1.83. Found: C, 70.67; H, 6.17; N, 2.01.

Characteristic singlets appeared in the highly shielded (upfield) region(−20 and −28 ppm) in the ³¹P NMR spectra and were assigned to thephosphorous atom in the diphenylphosphine groups attached to theferrocene ring (see FIG. 8). The presence of ferrocenyl ring protons inthe 3.5-4.5 ppm region, an axial methyl proton chemical shift (δ) at1.30 ppm, and three protons of the phenyl ring of dopamine at 6.20, 6.39and 6.60 ppm confirmed the formation of the desired compound (see FIG.7). This compound was further characterized by FAB-mass spectrometry andexhibited the characteristic molecular ion peak (m/z=733.196) (see FIG.9).

Synthesis of Fe₃O₄: Magnetite nanoparticles of 6-8 nm in size wereprepared by reaction of divalent and trivalent iron in a 1:2 ratio in analkaline medium at room temperature under an argon atmosphere withconstant stirring (500 rpm). The pH of the solution was held constantwith the periodic addition of conc. NH₄OH for 4 hours. A blackprecipitate was collected using a magnet and washed with DI waterseveral times to remove any unreacted iron precursors.

Synthesis ofFe₃O₄@{η³-C₃H₄-PPh₂}Fe{η⁵-C₅H₃-1-PPh₂-2-CH(Me)NH—CH₂—CH₂-4-Ph-1,2-OH}(Fe₃O₄@dop-BPPF): The magnetite nanoparticles (MNPs) were functionalized(see FIG. 1) using a previously reported procedure modified as follows:To a suspension of magnetic nanoparticles (200 mg) in anhydrouschloroform, dop-BPPF (200 mg) solution in dry methanol was added underan argon atmosphere. The mixture was sonicated in a bath sonicator for 6hours. The surface functionalized magnetic nanoparticles were collectedusing a magnet after repeated washing with methanol followed bycharacterization. FTIR in KBr (cm⁻¹): v=3435 (O—H+N—H), 2938 (arC—H),1428 (arC—C), 590 (Fe—O).

Ferrocenylphosphine was linked to the dopamine moiety, which was used asan anchoring unit to attach the complex onto the surface of the magneticnanoparticles. Bidentate enediol ligands provide higher stability andtight binding to iron oxide by transforming under-coordinated Fe surfacesites back to a bulk-like octahedral lattice structure foroxygen-coordinated magnetite, and this behavior is further supported bythe Langmuir isotherm, which indicated that the adsorption of dopaminemoiety via the 1,2-dihydroxyl functional group was more favorable thanits desorption from the metal nanoparticles surface (G. W. Gokel, I. K.Ugi, J. Chem. Educ. Chem. 49 (1972) 294-296; and L. X. Chen, T. Liu, M.C. Thurnauer, R. Csencsits, T. Rajh, J. Phys. Chem. B 106 (2002)8539-8546, each incorporated herein by reference in their entirety).

Synthesis ofFe₃O₄@{η⁵-c₅H₄-PPh₂}Fe{η⁵-C₅H₃-1-PPh₂-2-CH(Me)NH—CH₂—CH₂-4-Ph-1,2-OH}-M(Fe₃O₄@dop-BPPF-M):The suspension of the magnetite nanoparticles (100 mg) in chloroform wassonicated for 1 hour. The solution of [Rh(NBD)Cl]₂ (0.015 mmol),slightly excess, in dichloromethane was added to the suspension andstirred for 4 hours under argon atmosphere. The materials was collectedand washed with dichloromethane to remove unreacted metal precursor.

The same procedure was followed to prepare Fe₃O₄@dop-BPPF-Pd and[Rh(NBD)Cl]₂ was replaced with [Pd(C₃H₅)Cl]₂.

Example 3 Characterization of the Synthesized Complex, FunctionalizedMagnetic Nanoparticle, and Catalyst

FIGS. 1B, 1C, 1D, and 1E are the transmission electron micrographs ofFe₃O₄, Fe₃O₄@dop-BPPF, Fe₃O₄@dop-BPPF-Pd, and Fe₃O₄@dop-BPPF-Rh,respectively. The micrographs show that the nanoparticles arespherically-shaped and uniformly distributed. The average diameter was6-8 nm. The high-resolution transmission electron micrograph andselected area electron diffraction (SAED) image are shown in FIGS. 1Fand 1G, respectively. The interplanar distance was determined to beconsistent with the literature data (T. Rajh, L. X. Chen, K. Lukas, T.Liu, M. C. Thurnauer, D. M. Tiede, J. Phys. Chem. B 106 (2002)10543-10552, incorporated herein by reference in its entirety). The SAEDdata also revealed higher order crystallinity, which was furtherconfirmed by the X-ray diffraction (XRD) signature of the nanomaterial.The peaks located at 30.22°, 35.70°, 43.10°, 53.40°, 57.10° and 63.20°indicate the formation of a nanocrystalline cubic (Fd3m) spinel Fe₃O₄nanostructure (JCPDS card No. 01-075-0449) (N. Pinna, S. Grancharov, P.Beato, P. Bonville, M. Antonietti, M. Niederberger, Chem. Mater. 17(2005) 3044-3049, incorporated herein by reference in its entirety).Therefore, coating the nanoparticles with dop-BPPF followed bycomplexation with Pd/Rh did not alter the original crystal structure ofthe parent compound (Fe₃O₄). Qualitative and quantitative phase analyseswere carried out using the Rietveld method. The XRD patterns wererefined by the Rietveld method (see FIGS. 12A, 12B, 13A, 13B, 14A, 14B,15A, and 15B) and confirmed the formation of a single phase (thegoodness fit factor was close to 1) (see Table 1). The calculatedcrystallite size was determined to be approximately 8.5 nm for all ofthe samples, which was in good agreement with the size obtained from TEManalysis. The calculated lattice parameter was approximately 8.36 Å,which was close to that of bulk magnetite. Elemental maps, as shown inFIGS. 3A-3D, indicate the uniform anchoring of the ferrocenylphosphineligands and the complexed ligand with Rh and Pd on the surface of thenanoparticles. The presence of these elements was confirmed by the EDSresults (see FIGS. 16A and 16B).

The Fourier transform infrared (FTIR) spectroscopic data revealed avibration red shift of Fe—O by 7 nm from 583 nm for the parent magnetitewith a bare surface. The characteristic aromatic C—H stretching at 2938cm⁻¹ and aromatic C—C at 1428 cm⁻¹ confirmed the presence of dop-BPPF onthe surface.

The thermal stability of dop-BPPF was investigated, and the stepwiseweight loss profile was determined under an argon atmosphere in atemperature range of 25-600° C. (see FIG. 10). The amount of weight losswas determined to be approximately 14%, which indicated that the amountof loading on the nanoparticle surface was 0.2 mmol of dop-BPPF per gramof magnetic nanoparticles. These data were further confirmed by theamount of phosphine determined from the EDS results.

The recorded magnetic data revealed the superparamagnetic nature of allof the samples at room temperature (see FIG. 4A). Prior to coating, themagnetization of the bare surface of the magnetite (Fe₃O₄) was 67 emug⁻¹, and the magnetization the surface-coated nanoparticles(Fe₃O₄@dop-BPPF) was 58 emu g⁻¹. The saturation magnetization valueslightly decreased due to the coating with dop-BPPF and complexationwith Pd and Rh. It is important to note that the coercivity (Hc) andremanence (Mr) were not affected by the surface functionalization andcomplexation processes. The coating of dop-BPPF and presence of Pd/Rhdid not substantially affect the bulk magnetization, which is veryimportant for the separation process, and these data were furtherconfirmed by the physical use of a magnet near to the vial containingthe particles (see FIG. 4B).

TABLE 1 Structural, microstructural of magnetite Fe₃O₄ before and aftercoating and complexation with Pd and Rh. Crystallite Lattice sizeMicrostrain parameter Goodness (nm) (%) (Å) of fit Fe₃O₄ 8.4 0.3608.372(4) 1.0726 Fe₃O₄@dop-BPPF 8.5 0.478 8.365(4) 1.1276Fe₃O₄@dop-BPPF-Pd 8.6 0.500 8.363(4) 1.1079 Fe₃O₄@dop-BPPF-Rh 8.4 0.3408.359(4) 1.1300

TABLE 2 Magnetic properties investigation data of magnetite Fe₃O₄ beforeand after coating and complexation with Pd and Rh. Coercivity,Saturation H_(c) Remanence, M_(r) magnetization, M_(s) (Oe) (emu/g)(emu/g) Fe₃O₄ 3.965 0.802 68.03 Fe₃O₄@dop-BPPF 4.322 0.645 58.75Fe₃O₄@dop-BPPF-Rh 4.480 0708 56.00 Fe₃O₄@dop-BPPF-Pd 4.614 0.722 54.15

Example 4 Procedure for the Hydroformylation Reaction

This reaction was carried out in a functional fume hood fitted with goodsuction. The functionalized magnetic nanoparticles, Fe₃O₄@dop-BPPF-Rh(50 mg), styrene (1.0 mmol, 0.12 mL) and freshly distilled THF (10 mL)were added to a Teflon-lined autoclave equipped with a pressure gaugeand a mechanical stirrer under an argon atmosphere. Next, the inertatmosphere was replaced with a mild pressure release of CO/H₂ gas forthree cycles. Then, the autoclave was pressurized with CO/H₂ (1:1) at1000 psi, and the temperature was maintained at 45° C. After completionof the reaction, the pressure was released, and the sample was passedthrough a short silica gel column followed by injection into a gaschromatograph to determine the conversion and regioselectivity values.

The catalytic activity was evaluated using various substituted styrenesand n-alkenes at 45° C. with a mixture of carbon monoxide and hydrogen(1:1) under a pressure of 1000 psi. The results are shown in Table 3. Astudy on the reaction conditions was performed using styrene as a modelsubstrate. At 45° C., 85% conversion of styrene to the correspondingaldehyde was achieved with a branched (B) to linear (L) ratio of 8:1 at200 psi (entry #1). As the reaction temperature increased to 70° C., theyield improved but the regioselectivity was lost (entry #2). The solventpolarity played an important role in the selectivity. Based on theresults in Table 1, a more polar solvent negatively affected theselectivity. Among all of the tested solvents, dichloromethane was themost efficient solvent for this reaction. For example, although a highselectivity (B:L=17:1) was obtained by employing a pressure of 1000 psiin THF at 45° C., a substantial improvement was observed when the samereaction was performed in dichloromethane, and the regioselectivityincreased to 28:1 from 17:1 (entries #3 and 4) and to 52:1 from 14:1(entries #6 and 7) for styrene and 4-methylstyrene, respectively.

Styrene substituted with different electron-withdrawing and -donatinggroups were used as substrates for the hydroformylation reaction.Although no noticeable change in the reactivity was observed, a profoundeffect was observed for the selectivity. The selectivity ratio for thebranched to linear isomers of nitrostyrene and bromostyrene was 99:1(entries #10 and 11). The hydroformylation of styrene under solvent-freeconditions resulted in 86% conversion (entry #5) with 85% branchedisomer. Thus, this system can be employed as a green catalyst in thehydroformylation reaction without the use of any organic solvents. Forn-alkene, the reactivity of the catalyst was slow. The conversion of1-octene (entry #14) reached 85% but the linear aldehyde was formed(B:L=0:100). This result was consistent with previously reported data.Also, no hydrogenated product was observed in the Rh-catalyzedhydroformylation.

The recyclability of the catalysts was investigated by employing thereaction conditions described herein. After the first round ofcatalysis, the nanocatalysts were washed with dichloromethane to removeany unwanted materials and reused for the 2^(nd) round of catalysiswithout the addition of more Rh metal precursor. A gradual loss in thecatalytic activity was observed after the 4^(th) run, which may be dueto the high pressure being employed in the reaction system, and theactive catalyst was leached from the surface of the magneticnanoparticles.

TABLE 3 Hydroformylation^(a) of olefins using Fe₃O₄@dop-BPPF and[Rh(NBD)Cl]₂ metal precursor.

Time Pressure Temp Conv.^(b) Branch. Linear Ratio Entry Substrate (h)(psi) Solvent (° C.) (%) (B) (L) (B:L) 1 Styrene  9  200 THF 45 85 88.611.4 8 2 Styrene 10  200 THF 70 91 48.1 51.9 0.9 3 Styrene  8 1000 THF45 >99 94.5 5.5 17 4 Styrene  8 1000 DCM 45 >99 96.4 3.6 28 5 Styrene 141000 No solv. 45 86 85.4 14.6 6 6 4- 14 1000 THF 45 >99 93.4 6.6 14Methylstyrene 7 4- 14 1000 DCM 45 >99 98.1 1.9 52 Methylstyrene 84-Vinylanisole 14 1000 DCM 45 >99 97.2 2.8 35 9 4-Chlorosyrene 12 1000DCM 45 >99 98.6 1.4 70 10 3-Nitrostyrene 13 1000 DCM 45 >99 99 1 99 112- 13 1000 DCM 45 >99 99 1 99 Bromostyrene 12 Vinylbenzoate 16 1000 DCM45 96 13 1-Octene 16 1000 DCM 45 85 — 100 −100 ^(a)1 mmol of styrene in10 mL anhydrous solvent under syn gas (CO:H₂ 1:1) pressure using 50 mgof Fe₃O₄@dop-BPPF-Rh and Rh-metal precursor ^(b)determined by GC andidentified by GC-MS; nd: not determined

Example 5 Procedure for the Mizoroki-Heck Reaction

This reaction was performed in a reaction tube fitted with a magneticstirrer and a Teflon stopper, and the reaction tube was in a parallelreactor. To a suspension of the catalyst, Fe₃O₄@dop-BPPF-Pd (50 mg), inDMF:water (1:1) (10 mL), styrene (1.0 mmol, 0.12 mL) and potassiumhydroxide (1.0 mmol, 56 mg) were added. The temperature was maintainedat 90° C. The progress of the reaction was monitored by a gaschromatograph, which was connected to a mass detector, and the productwas extracted using ethyl acetate. The concentrated solution was passedthrough a short silica gel column and eluted with hexane:ethyl acetate(9:1).

In a study of the reaction conditions of the Mizoroki-Heck reaction,styrene and iodobenzene were chosen as the model substrates to evaluatethe catalytic activity. The results are shown in Table 4. The effect ofthe temperature was investigated. A higher temperature was determined tobe effective, which was confirmed by the results in entries #1 and 2. At95° C., styrene was quantitatively converted to its correspondingproduct. However, at a lower temperature, the conversion was 50% (entry#1). In this reaction, the base played a crucial role in theregeneration of Pd active species. Therefore, K₂CO₃, Et₃N and KOH wereused in the DMF:H₂O (1:1) solvent mixture, and the highest conversionwas obtained using KOH (entry #2) compared to that using potassiumcarbonate or triethylamine (entries #3 and 4). The solvent effect wasinvestigated by employing a series of solvent systems, such as water,toluene, DMF, and DMF:water (1:1). The catalytic yield in pure water wasonly 67% (entry #5), which may be due to the insolubility of organicsubstrate in water and thus the substrate was not able to contact themetal reaction sites effectively. However, the DMF:water (1:1) mixturewas a better solvent compared to that of pure DMF (entries #2 and 7).

TABLE 4 A study of the reaction conditions of the Mizoroki-Heck reactionbetween iodobenzene and styrene.

Temp Conversion^(a) Entry Base (° C.) Solvent (%) 1 KOH 60 DMF-H₂O (1:1)50 2 KOH 95 DMF-H₂O (1:1) 99 3 K₂CO₃ 95 DMF-H₂O (1:1) 69 4 Et₃N 95DMF-H₂O (1:1) 56 5 KOH 95 H₂O 67 6 KOH 95 Toluene 44 7 KOH 95 DMF 81^(a)Conversion measured after 30 minutes of reaction Yields are based oniodobenzene; ^(b)determined by GC and identified by GC-MS

Using the reaction conditions described above, the coupling reaction wasextended to a range of substituted styrene substrates to explore thescope of the newly developed catalytic system, and the results aresummarized in Table 5. Bromobenzene was much less reactive with styrenethan the corresponding iodobenzene (entries #1 and 2). However,prolonging the reaction time to 2-24 hours resulted in quantitativeconversion. This result indicated the catalyst was stable for theextended reaction time. The electron-withdrawing group in the para andmeta positions of styrene (entries #7-10) decreased the reaction rate.For example, using 4-chlorostyrene (entries #7 and 8), the maximumconversion was 69% after 24 hours, and the same trend was observed for3-nitrostyrene (entry #10), which yielded 85% of the coupling product.Also, no biphenyl product was observed in the Pd-catalyzed Mizoroki-Heckreaction.

The reusability of the nanocatalysts was investigated using the reactionof styrene and iodobenzene at 95° C., in a DMF:water 1:1 solventmixture, and KOH base. The results are shown in FIG. 5 as a bar chart.After completion of the coupling reaction, the catalyst was collected byplacing an external magnet at the bottom of the reaction vessel, and thesolution was decanted for work up and gas chromatography. The collectedcatalyst particles were repeatedly washed with ethyl acetate and waterprior to use in the next round of catalysis. The catalyst exhibited aconsistent activity up to the 10^(th) consecutive cycle after thereaction time was increased to 12 hours. Intrigued by its robustness,the collected catalysts from the 10^(th) cycle were placed in the samecoupling reaction for 30 days, and surprisingly, the observed loss ofactivity remained almost the same.

TABLE 5 A study of the reaction conditions for the Mizoroki-Heckreaction^(a) between aryl halide and substituted styrene.

Substrate Halide Time Entry (R) (X) (min) Conversion^(b) 1 H I 30 99 2 HBr 30 78 60 80 120 96 24 h 99 3 4-CH₃ I 30 96 4 4-CH₃ Br 30 87 60 95 12098 5 4-OCH₃ I 30 99 6 4-OCH₃ Br 30 77 60 94 120 96 7 4-Cl I 30 98 8 4-ClBr 30 35 60 60 120 66 24 h 69 9 3-NO₂ I 30 94 60 97 10 3-NO₂ Br 30 22 6027 24 h 85 11 2-Br I 30 96 ^(a)reactions were carried out at 95° C. inDMF:H₂O (1:1) using KOH as base and Fe₃O₄@dop-BPPF-Pd; yields are basedon halobenzene; ^(b)determined by GC and identified by GC-MS

The invention claimed is:
 1. A ferrocenyl complex represented by any ofthe following formulas Formula (IA), Formula (IB), Formula (IIA), orFormula (IIB):

where each of R¹, R², R³, R⁴, and R⁵ is independently a hydrogen, anoptionally substituted alkyl, or an optionally substituted aryl; R^(5′)is a hydrogen, hydroxy, an optionally substituted alkyl, an optionallysubstituted aryl, an optionally substituted arylalkyl, an optionallysubstituted alkoxy, an optionally substituted cycloalkyloxy, anoptionally substituted aryloxy, or an optionally substituted arylalkoxy;each of R⁶ and R⁷ is independently a hydrogen, an optionally substitutedalkyl, an optionally substituted aryl, an optionally substitutedarylalkyl, an optionally substituted alkoxy, an optionally substitutedaryloxy, or an optionally substituted arylalkoxy; each of R⁸ is anoptionally substituted alkyl, or an optionally substituted aryl; a and bare independently an integer in a range of 1-10; X is O or NH; M isiron; and W is an optionally substituted arylene.
 2. The complex ofclaim 1, wherein R¹ is an optionally substituted alkyl.
 3. The complexof claim 1, wherein R⁸ is an optionally substituted aryl.
 4. The complexof claim 1, wherein X is NH.